The amount of information handled by various electronic apparatuses has been explosively increasing with the progress of information society in recent years. Thus, storage devices used in such electronic apparatuses are required to have further improved performance.
Among the devices, as memory elements to be substituted for NOR flash memories, DRAMs or the like that are generally used at present, magnetic random access memories (MRAMs), particularly, magnetic random access memories (MRAMs) (or spin torque-magnetic random access memories (ST-MRAMs)) that use spin torque magnetization reversal (which is also called spin injection magnetization reversal), have gained attention. The ST-MRAMs are considered to be capable of realizing low power consumption and large capacity while maintaining advantages of MRAMs which are operations at high speeds and a substantially indefinite number of rewriting operations.
Although an ST-MRAM is configured such that a plurality of memory cells, each including a magnetoresistive element serving as a storage element that stores information of 1/0 are arrayed therein, an element having a magnetic tunnel junction (MTJ) structure has been used as the magnetoresistive element. The MTJ structure is a structure in which a non-magnetic material layer (a tunnel barrier layer) sandwiched between two magnetic material layers (a magnetization fixed layer and a storage layer). A magnetoresistive element with the MTJ structure will also be referred to as an MTJ element hereinbelow. In an MTJ element, information of 1/0 is recorded by using spin torque magnetization reversal in the storage layer generated by causing a current to flow in the MTJ structure.
Here, in order to put memory elements having the MTJ structure into practical use, a process technology of patterning the MTJ structure is necessary in order not to cause damage, short-circuiting, and current leakage. However, it is difficult to pattern the MTJ structure through etching. Since transition metals, for example, are used as a material that forms a magnetic material layer in most cases, in a metal etching technology using a halogen-based gas that is widely used in an etching process of silicon-based semiconductor devices, it is not possible to easily etch the magnetic material layer. If a reactive ion etching (RIE) method or an ion beam etching method is used, although the magnetic material layer can be easily etched, there is grave concern of a short circuit or current leakage occurring because of an etched product adhering to a side wall of the tunnel barrier layer.
Thus, in patterning of the MTJ structure, a method in which etching of a magnetic material layer formed in a higher layer than a tunnel barrier layer (which will also be referred to as an upper magnetic material layer below) is stopped halfway, a part of the upper magnetic material layer is oxidized in a state in which the upper magnetic material layer remains, and thereby a region with neutralized magnetism and deteriorating conductivity (which will also be referred to as a neutralized region below) is formed has been proposed.
In the technology disclosed in Patent Literature 1, for example, patterning of the upper magnetic material layer is performed in the following procedure. That is, first, a first magnetic material layer, a non-magnetic material layer, a second magnetic material layer (which corresponds to an upper magnetic material layer), and a connection layer for connecting a cap layer and an electrode are sequentially laminated on a substrate. Next, a mask layer patterned in a predetermined shape is formed on the connection layer. Next, a region not covered by the mask layer is etched to a depth at which a thickness of the second magnetic material layer is about half. Next, the second magnetic material layer remaining in the etched region is oxidized, and thereby a neutralized region having deteriorating magnetic properties and conductivity is formed. Then, the neutralized region is reduced.
According to the technology disclosed in Patent Literature 1, since the etched surface does not reach the tunnel barrier layer, no etched products adhere to a side wall of the tunnel barrier layer, and thus occurrence of a short circuit and current leakage can be avoided. In addition, since the neutralized region is reduced after the neutralized region is formed through the oxidization, the problem that excessive oxygen remaining in the neutralized region expands due to heat treatment in the following manufacturing steps and damages the neutralized region can be solved.